External application of active ingredients has been intended to produce local effects, such as bactericidal effects, disinfectious effects, analgesic effects, antipsoraic effects, antiinflammatory effects, and the like, onto the skin or subcutaneous tissues.
On the other hand, oral administration or injection commonly aims at producing systemic effects. Oral administration sometimes associates with problems that the absorbed active ingredient is susceptible to primary metabolism in the liver and that the oral administration of active ingredient in order to assure long-lasting effects gives- temporary higher than desired blood level, resulting in unfavorable side effects. Further, some active ingredients, for example, Indometacine, cause gastrointestical disorders when administered orally.
Administration by injections achieves rapid absorption of active ingredients but requires specialists, such as physicians.
In order to overcome the above-described disadvantages of oral administration or injection, percutaneous administration aiming at systemic effects has recently been proposed. Percutaneous administration of active ingredients is advantageous in that desired blood level of active ingredients can be maintained easily so that duration of therapy can be easily controlled and that primary metabolism of active ingredient by the liver can be eliminated.
However, since normal skin naturally has a barrier function to prevent entrance of a foreign matter into the body, normal skin is relatively impermeable to most therapeutic agents in that desired blood levels of the therapeutic agent cannot be achieved by means of percutaneous absorption. The percutaneous absorption of therapeutic agents can, however, be enhanced by means of adjuvants or penetration enhancers, and various kinds of penetration enhancer have been proposed in recent years. For example, U.S. Pat. No. 3,551,554 discloses dimethyl sulfoxide as well as dimethylacetamide, dimethylformamide, methyldecyl sulfoxide, etc.
There are also known penetration enhancer compositions, such as a combination of dimethylacetamide with ethyl alcohol, isopropyl alcohol or isopropyl palmitate as disclosed in U.S. Pat. No. 3,472,431; a combination of 2-pyrrolidone with an suitable oil and an alcohol ester of a straight chain fatty acid as disclosed in U.S. Pat. No. 4,017,641; and the like. However, none of these penetration enhancer is satisfactory in effect, safety, and feel on use.